Mx0 and Eden no Ori.
Mx0 being my number one favorite manga but got canceled, it was pretty popular in Japan with it's Tankobon sales being in top 10, if they were to revive this as an anime I would be extremely happy.

Eden no Ori another manga that just ended after being canceled, it got over 180 chapters which is enough to make 2 seasons without fillers.

Ping Pong, Nausica (the movie did not do it justice since the manga was just a segway to make a movie, should be given a proper 40 episode series), Cromartie High needs more of the anime, No. 5, Scott Pilgrim, GoGo Monster, and some of the Zelda titles.